Microscopic examination revealed a cellular tumor with scattered foci of necrosis (Fig. 2). The neoplasm had a complex structure: its cells were closely intermingled with abundant network of capillary vessels with densely sclerotic walls (Fig. 3). These cells were ovoid-to round but their size varied. Some of them resembled oligodendrocytes - they had round outline and clear to slightly eosinophilic cytoplasm and small vesicular nucleus with small nucleolus. Other cells were larger, multinucleated and presented anisonucleosis and nuclear hyperchromasia (Fig. 3). Mononuclear and multinucleated ganglioid cells were also present; their nuclei resembled those of mononuclear cells. Scattered preexistent ganglion cells were visible at the marginal portion of the tumor (Fig. 4) and multinucleated giant sarcomatous cells were focally present among the neurocytoma cells (Fig. 5). Apoptotic figures were present within the necrotic foci and around these areas glomeruloid vascular proliferations were present (Fig. 2). Mitotic figures were not seen.
Immunohistochemical study revealed reactivity for synaptophysin in most of the mononuclear and multinucleated cells (Fig. 6). GFAP staining identified single reactive astrocytes scattered in the tumor mass. Neurofilament protein was not present in the neoplastic cells. CD34 antigen was found in some of the endothelial cells lining hyalinized vascular channels. Ki-67 (MIB-1) index in the tumor cells was 0.7%. Ultrastructural analysis disclosed some dense-core granules and abortive synapses in the neoplastic cells.